Discharge lamps produce light by ionizing a filler material such as a mixture of metal halides and mercury with an electric arc passing between two electrodes. The electrodes and the filler material are sealed within a translucent or transparent discharge chamber or arc tube which contains and maintains the pressure of the energized filler material and allows the emitted light to pass through it. The filler material emits a desired spectral energy distribution in response to being excited by the electric arc. For example, halides produce spectral energy distributions that offer a broad choice of light properties, e.g. color temperatures, color renderings, and luminous efficacies.
Historically, the arc tube in a discharge lamp was formed from fused quartz, which was then shaped into desired geometric shapes. However, fused quartz had disadvantages resulting from its reactive properties at high operating temperatures. Thus ceramic arc tubes were developed to operate at higher temperatures for improved color temperatures, color renderings, and luminous efficacies, while significantly reducing reactions with the filler material.
Conventionally, ceramic arc tubes have been constructed from multiple parts that are extruded or die pressed from a ceramic powder. The multitude of parts are assembled by placing and bonding them together to form a complete arc tube. This process has numerous disadvantages. For example, a defect may be present in a single part thus rendering the entire arc tube defective. Furthermore, a leak may occur between two improperly bonded parts.
A manufacturing process is desirable to manufacture a one-part or integrally formed arc tube.